THE IMPLICATIONS OF THE EVIDENCE
The effects associated with family size on the well-being of individuals-primarily the children-in a family are varied, but serious: increased illness, including malnutrition, serious enough in younger children to increase mortality rates; less satisfactory growth and intellectual development; increased illness in the parents, as well as clear-cut economic and emotional stresses. Family size is not the only cause of these effects, but it is clearly implicated as an important element in the interacting network of causal factors.
The evidence regarding the effects of birth interval is less extensive than that relating to family size but no less disconcerting. At first glance the effects appear to be quite similar—increased mortality, increased morbidity, less satisfactory growth, and less adequate intellectual development. It appears, in fact, that excessive crowding of children—too many children too quickly—in a family with a young mother will produce the same effects quickly that excessive numbers of children will produce more slowly in larger families.
Do these effects matter? Are the consequences of excessive family size or inadequate spacing of children at the family level sufficiently serious to be of concern to policymakers or economic planners? What is needed for a confident answer to such questions is data that would allow us to move from the qualitative description of effects provided by the evidence available to quantitative estimates of the overall impact of such effects. Such data are not available. In a way this is not surprising. Gunnar Myrdal, an internationally preeminent economist, was compelled, because of a similar lack of data, to justify the provision of health care in developing countries as a "moral imperative" in his monumental Asian Drama (75). In the light of the evidence we have seen, one might equally well consider the limitation of family size or the better spacing of children a "moral imperative."
One can, in fact, make some quantitative estimates with the data available-even while acknowledging the need for better information. Given the data from Scotland that the average I.Q. of children with five or more siblings is 91, 22 points below that of only children, what are the implications for developing countries? In Candelaria, Colombia, we found that 27 percent of the preschool children had five siblings or more. The implication of the association between family size and intelligence is such that it suggests that a fourth of the population may be subject to serious impairment of its intellectual development. Evidence from the United States has a direct bearing here; the President's Task Force on Manpower Conservation, appointed to investigate why so many youths were unfit for military service, found (.hat 47 percent of all young men rejected on mental grounds came from families with six or more children (76). Similar quantitative data were provided by Pasamanick and Lilienfield (77) in their examination of maternal and fetal